1. Field of the Invention
The invention pertains to a winding method for the non-radial winding of a cathode tube deflector.
2. Description of the Prior Art
Aligned-gun trichromatic cathode tubes are presently fitted with deflectors which themselves perform the self-convergence of electron beams and correct image geometry. The line field created by saddle-shaped coils is called a "positive astigmatic" field while the frame field is called a "negative mean astigmatic" field when it ensures convergence and a "positive front astigmatic" field when it performs geometry corrections.
Several methods are used in the field of wide-audience television applications to make a frame winding according to the above-mentioned requirements: it is possible to use either a saddle-shaped coil or a doughnut coil. The doughnut coil can be made either with a radial frame that works with field formers (ferromagnetic parts attached to the deflector) or by using an inclined winding method with a rear angle greater than the front angle, a coil of this type being possibly also associated with magnetic correcting means. In this latter, widely-used method, one of the following three techniques is employed for the winding:
Plastic parts with notches are fixed to the front and rear of the ferrite core, and these notches determine the inclination of the winding wire. This method gives sharp inclinations for the wire but is expensive because it requires the use of special parts and entails additional operations to handle these parts, thus increasing production time;
The wire is wound on the bare ferrite core which may be notched, but the inclination of the wire is then greatly limited (to a maximum of about 15.degree.), for the wire tends to slip in a generally dissymmetrical way;
Or, finally, to prevent the wire from slipping, adhesive elements are placed on the ferrite core at the front and rear planes. These elements may be adhesive tapes, glues, waxes, etc. This type of method is costly. Its automation is difficult and it does not give the wire inclinations of more than about 20.degree..
3. Summary of the Invention
An object of the present invention is a winding method used to obtain inclinations in the winding wire which reach about 30.degree. at the edges of the coil, on bare ferrite cores without notches, without adding any parts or any adhesive element, the said method being easily automated.
The method according to the invention consists in making a first layer of the coil in a manner which is at least approximately radial, with a wide coil pitch and then in depositing the following non-radial layers by using at least a portion of the wires of the first layer to prevent the following layers from slipping.